Patients often wish to remain mobile or ambulatory while also receiving oxygen. This generally requires the oxygen delivery apparatus to be portable. To be portable, the oxygen or gas delivery apparatus preferably has to be compact and relatively lightweight. This is especially important since many patients needing oxygen are already frail or of limited physical capacity. One approach to such portability has been to store the oxygen or gas under pressure in gas cylinders, and such gas cylinders are equipped with pressure regulators, flow meters, and other apparatus for delivering the desired flow of oxygen to the patient. The need to make such high pressure gas cylinders smaller for ambulatory uses has meant a corresponding increase in the pressures applied to gases in such cylinders. The transportation and use of such high-pressure devices may require special handling in ambulatory or home-based settings.
Furthermore, even when gas has been compressed to 2,000 PSI, the compact cylinders need to be changed relatively frequently. This reduces the “range” that a patient may have with this high-pressure gas cylinder type of apparatus.
To lengthen the effective life of an oxygen delivery apparatus, manufacturers have resorted to so-called “cryogenic systems” or “liquid systems.” These systems make use of liquid oxygen as opposed to merely using pressurized oxygen in the gas phase. Liquid oxygen is generally 860 times more compact than typical pressurized gas. Cryogenic systems generally involve a thermal flask or cryogenic chamber. Such flasks or chambers include an inner vessel containing liquid oxygen. This inner vessel is surrounded by an outer casing and, importantly, between the outer casing and inner vessel, a vacuum is generally established to improve the insulative properties of the thermal flask.
In operation, cryogenic systems of the current art usually draw off a predetermined quantity of liquid oxygen which is then sent through a series of warming coils. As the liquid oxygen travels through the warning coils, it changes phase and evaporates into oxygen gas. The warming coils thus are often critical to transforming the liquid oxygen drawn from the flask into oxygen gas at an appropriate temperature to be inhaled by the patient.
Unfortunately, the systems of the current art suffer from various drawbacks and disadvantages. For example, the warming coils used in current systems have various difficulties, complexities, and other shortcomings. Coils often are bulky. Warming-coil-type apparatus may, under certain circumstances, be mishandled or otherwise operated imprudently with the result that liquid oxygen from inside the container is depleted too quickly or escapes inadvertently to potentially “burn” the users.